JP2003007301A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous electrolyte secondary battery having improved cycle characteristics, and particularly excellent in cycle characteristics under a temperature condition exceeding room temperature. SOLUTION: In a non-aqueous electrolyte secondary battery 1 including a positive electrode 2 containing a positive electrode active material, a negative electrode 4 containing a negative electrode active material capable of inserting and extracting lithium, and a non-aqueous electrolyte, the rubidium compound contains It is contained in at least one of the positive electrode 2 and the negative electrode 4. This prevents cations that adversely affect the negative electrode from being generated in the positive electrode due to the charge / discharge reaction under a temperature condition exceeding room temperature.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material capable of inserting and extracting lithium, and a non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years, with the breakthrough of various electronic devices, research on a secondary battery which can be charged and discharged as a power source that can be used conveniently and economically for a long time is in progress. Lead storage batteries, alkaline storage batteries, lithium secondary batteries, and the like are known as typical secondary batteries. Among these secondary batteries, lithium-based secondary batteries have advantages such as high output and high energy density, and are used as practical batteries.

A lithium secondary battery has, as main constituent elements, a positive electrode using an active material that reversibly electrochemically reacts with lithium ions, and a material capable of inserting and extracting lithium, a negative electrode containing metallic lithium or lithium. , A non-aqueous electrolyte such as a non-aqueous electrolyte. Then, the discharge reaction of the lithium-based secondary battery generally proceeds by the lithium ions being eluted into the non-aqueous electrolyte at the negative electrode and the lithium ions being intercalated between the layers of the active material at the positive electrode. On the other hand, in the charging reaction of the lithium secondary battery, the reverse reaction of the discharging reaction proceeds, and lithium ions are deintercalated in the positive electrode. That is, the charge / discharge reaction of the lithium secondary battery is based on a reaction in which lithium ions supplied from the negative electrode enter and leave the positive electrode active material.

[0004]

By the way, the battery life of a lithium secondary battery is closely related to the deterioration of cycle characteristics. Therefore, in order to extend the battery life of the lithium secondary battery, it is necessary to suppress deterioration of cycle characteristics. Up to now, attempts have been made to improve the cycle characteristics of lithium-based secondary batteries, but the current situation is that they have not been sufficiently improved. In particular, deterioration of cycle characteristics in an environment exceeding room temperature has not been improved yet.

The problem of deterioration of battery performance under an environment exceeding room temperature is a problem to be particularly noted in the case of a large lithium secondary battery for an electric vehicle or load leveling. This is because the heat generated inside the battery during charging / discharging increases in proportion to the increase in size of the battery, and the temperature inside the battery may become relatively high even when the environmental temperature is near room temperature. In addition, even in the case of a small lithium-based battery used as a power source for a small portable electronic device, considering that it is used in a closed room environment such as in an automobile under hot weather, battery characteristics in an environment exceeding room temperature It is very important to prevent the deterioration of the.

In view of such conventional circumstances, the present invention has been proposed for the purpose of providing a non-aqueous electrolyte secondary battery having improved cycle characteristics and particularly excellent cycle characteristics under a temperature condition exceeding room temperature. It is a thing.

[0007]

Means for Solving the Problems As a result of intensive studies made by the present inventors in order to achieve the above-mentioned object, as a result of charge / discharge reaction of a non-aqueous electrolyte secondary battery under a temperature condition exceeding room temperature, a positive electrode At a cation other than the ions contributing to the charge / discharge reaction, for example, a cation other than a lithium ion, specifically, a cation of a metal such as Co that constitutes the positive electrode active material (hereinafter,
It is simply called a cation. ), This cation adversely affects the negative electrode and deteriorates the cycle characteristics. Therefore, they have found that suppressing the generation of cations in the positive electrode can improve the cycle characteristics of the non-aqueous electrolyte secondary battery under temperature conditions exceeding room temperature.

The present invention has been completed based on such findings, and comprises a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material capable of inserting and extracting lithium, and a non-aqueous electrolyte. In the non-aqueous electrolyte secondary battery, the rubidium compound is contained in at least one of the positive electrode and the negative electrode.

The rubidium compound is a substance capable of stably generating an oxidation state, and dissolves in the electrolyte as rubidium ion (Rb ⁺ ) under a temperature condition exceeding room temperature.
When rubidium ion (Rb ⁺ ) elutes in the electrolyte,
The ionic equilibrium suppresses the production of other cations. Therefore, when at least one of the positive electrode and the negative electrode contains the rubidium compound, generation of cations in the positive electrode is suppressed. Further, the rubidium ion generated in the positive electrode is a cation, but it has a property of being absorbed by the negative electrode and is absorbed by the negative electrode and loses its activity as a cation, so that it is harmless inside the battery.

Therefore, in the non-aqueous electrolyte secondary battery according to the present invention, cations which adversely affect the negative electrode are prevented from being generated in the positive electrode, and the cycle characteristics under the temperature condition exceeding room temperature are compared with those of the conventional one. Then it will be improved and become better.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a non-aqueous electrolyte secondary battery according to the present invention will be described in detail with reference to the drawings.

Non-aqueous electrolyte secondary battery 1 to which the present invention is applied
Is a so-called lithium-ion secondary battery having a coin shape, and as shown in FIG. 1, a positive electrode 2, a positive electrode can 3 containing the positive electrode 2, a negative electrode 4, and a negative electrode can 5 containing the negative electrode 4. , Separator 6 disposed between positive electrode 2 and negative electrode 4
And an insulating gasket 7, and comprises a positive electrode can 3 and a negative electrode can 5.
Is filled with a non-aqueous electrolyte.

By the way, in the conventional non-aqueous electrolyte secondary battery, cations other than ions contributing to the charge / discharge reaction at the positive electrode along with the charge / discharge reaction, that is, cations other than lithium ions, specifically, the positive electrode active material. Occasionally, a cation of a metal such as Co (hereinafter, simply referred to as a cation) that composes is generated. Since this cation adversely affects the negative electrode, there is a problem that the cycle characteristics of the non-aqueous electrolyte secondary battery are deteriorated.

On the other hand, in the non-aqueous electrolyte secondary battery 1 to which the present invention is applied, at least one of the positive electrode 2 and the negative electrode 4 contains a rubidium compound.

The rubidium compound is a substance capable of stably generating an oxidation state, and dissolves in the electrolyte as rubidium ion (Rb ⁺ ) under a temperature condition exceeding room temperature.
When rubidium ion (Rb ⁺ ) elutes in the electrolyte,
The ionic equilibrium suppresses the production of other cations. Therefore, since at least one of the positive electrode 2 and the negative electrode 4 contains the rubidium compound, the positive electrode 2
The production of cations in is suppressed. Further, the rubidium ion generated in the positive electrode 3 is a cation, but has a property of being absorbed by the negative electrode 4 and is absorbed by the negative electrode 4 and loses its activity as a cation. It is harmless inside the secondary battery 1.

Therefore, in the non-aqueous electrolyte secondary battery 1, cations that adversely affect the negative electrode 4 are prevented from being generated in the positive electrode 2, and the cycle characteristics under a temperature condition exceeding room temperature are higher than those of the conventional ones. Improved and better.

As the rubidium compound, at least one of rubidium oxide, rubidium sulfate and rubidium fluoride is used.

It is appropriate that the rubidium compound is contained in the positive electrode 2, and the addition amount of the rubidium compound is 2 in the positive electrode 2.
It is suitable that it is in the range of not less than 10% by weight and not more than 10% by weight. When the amount of the rubidium compound added to the positive electrode 2 is less than 2% by weight, the effect of stably generating a high oxidation state and suppressing the generation of cations in the positive electrode 2 cannot be sufficiently obtained, and the cycle characteristic improving effect is obtained. May be insufficient. On the other hand, when the amount of the rubidium compound added to the positive electrode 2 exceeds 10% by weight, the proportion of the positive electrode active material in the positive electrode 2 becomes small, and the discharge capacity necessary for a practical battery may not be achieved. Therefore,
By setting the addition amount of the rubidium compound within the above range, the generation of cations in the positive electrode 2 is sufficiently suppressed, so that the cycle characteristics of the non-aqueous electrolyte secondary battery 1 are improved, and particularly in an environment exceeding room temperature. The cycle characteristics below are excellent.

The positive electrode 2 has a positive electrode active material layer containing a positive electrode active material formed on a positive electrode current collector made of metal such as aluminum foil.

As the positive electrode active material, a metal oxide, a metal sulfide, a polymer, or the like is used. For example, TiS ₂ ,
MoS ₂ , NbSe ₂ and V ₂ O ₅ can be used. In addition, the discharge potential is high and the energy density of Li _x C is high.
A lithium composite oxide such as o _y O ₂ (here, the value of x changes depending on charge and discharge, but usually, x and y are about 1 at the time of synthesis) can also be used as the positive electrode active material.

The positive electrode can 3 accommodates the positive electrode 2 and serves as an external positive electrode of the non-aqueous electrolyte secondary battery 1.

In the negative electrode 4, a negative electrode active material layer containing a negative electrode active material capable of inserting and extracting lithium is formed on a negative electrode current collector made of, for example, nickel foil.

As the negative electrode active material, metallic lithium, a lithium alloy, a conductive polymer doped with lithium (for example, polyacetylene, poropyrrole, etc.), an intercalation compound in which lithium ions are incorporated into a crystal, and a carbon capable of absorbing and desorbing lithium. Etc. can be used.

The negative electrode can 5 accommodates the negative electrode 4 and serves as an external negative electrode of the non-aqueous electrolyte secondary battery 1.

As the non-aqueous electrolyte, a liquid non-aqueous electrolyte prepared by dissolving an electrolyte salt in a non-aqueous solvent, that is, a so-called non-aqueous electrolytic solution is used.

As the non-aqueous solvent, any solvent conventionally used in this type of non-aqueous electrolyte secondary battery can be used. For example, propylene carbonate, ethylene carbonate, butylene carbonate and high-dielectric constant solvents can be used. γ-butyrolactone, etc.
Low-viscosity solvents such as 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl carbonate, methylethyl carbonate and diethyl carbonate can be used. As these non-aqueous solvents, only one kind may be used alone, or a plurality of kinds may be mixed and used.

The electrolyte salt generally differs depending on the conducting ion species, but when the conducting ion species is lithium ion, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiB.
F ₄ and CF ₃ SO ₃ Li can be used. As these electrolyte salts, only one kind may be used alone, or a plurality of kinds may be mixed and used.

As the separator 6, any conventionally known material such as a microporous sheet made of an olefin polymer material such as polyethylene or polypropylene can be used.

The insulating gasket 7 is incorporated in and integrated with the negative electrode can 5. The insulating gasket 7 is for preventing leakage of the nonaqueous electrolytic solution filled in the negative electrode can 5 and the positive electrode can 3.

In the non-aqueous electrolyte secondary battery 1 configured as described above, at least one of the positive electrode 2 and the negative electrode 4 contains a rubidium compound which is a substance capable of stably generating an oxidation state. Therefore, generation of cations in the positive electrode 2 is suppressed along with the charge / discharge reaction in an environment exceeding room temperature. Therefore, the non-aqueous electrolyte secondary battery 1
Has excellent cycle characteristics especially under temperature conditions exceeding room temperature.

In the above description, the coin-shaped non-aqueous electrolyte secondary battery 1 has been described, but the battery system of the present invention is not limited to this, and a cylindrical type, a square type,
Various battery shapes such as button type can be adopted.

In the above description, a battery using a liquid non-aqueous electrolyte as the non-aqueous electrolyte, that is, a non-aqueous electrolyte, has been described, but the present invention is not limited to this, and an electrolyte salt is dispersed in a matrix polymer. The present invention is also applicable to a lithium-based secondary battery including a solid electrolyte obtained by the above, a gel electrolyte obtained by swelling a matrix polymer with a non-aqueous electrolytic solution, and the like.

[0033]

EXAMPLES The non-aqueous electrolyte secondary battery to which the present invention is applied will be described in detail below with reference to specific experimental results.

Sample 1 First, 90 parts by weight of lithium cobalt oxide as a positive electrode active material, 5 parts by weight of conductive carbon as a conductive agent, and 5 parts by weight of polyvinylidene fluoride as a binder were mixed.
Further, it was dispersed in a solvent to prepare a positive electrode mixture paint. Next, the positive electrode mixture coating material was applied onto an aluminum foil serving as a positive electrode current collector to form a positive electrode mixture layer having a thickness of 100 μm. In this way, a positive electrode including the positive electrode mixture layer and the positive electrode current collector was produced.

Next, 90 parts by weight of hard carbon was used as the negative electrode active material, and 1 part of polyvinylidene fluoride was used as the binder.
0 parts by weight was mixed and further dispersed in a solvent to prepare a negative electrode mixture coating material. Next, the negative electrode mixture coating material was applied onto a copper foil serving as a negative electrode current collector to form a negative electrode mixture layer having a thickness of 100 μm. In this way, a negative electrode including the negative electrode mixture layer and the negative electrode current collector was produced.

Next, LiPF ₆ as an electrolyte salt was dissolved in a mixed solvent of propylene carbonate (PC) and ethylene carbonate (EC) to prepare a non-aqueous electrolytic solution.

Next, the negative electrode was placed in a negative electrode can, and a nonaqueous electrolytic solution was injected into the negative electrode can, and then a separator was placed on the negative electrode.
Next, a positive electrode was placed on the separator and the nonaqueous electrolytic solution was injected, and then the positive electrode can was caulked and fixed to the negative electrode can via a gasket, to fabricate a coin-type nonaqueous electrolytic secondary battery.

Samples 2 to 8 In the same manner as in Sample 1, except that rubidium oxide was added to the positive electrode, and the content of the positive electrode active material and the amount of rubidium oxide added were changed as shown in Table 1 below. A non-aqueous electrolyte secondary battery was produced.

Samples 1 to 8 produced as described above were charged to a final voltage of 4.2 V with a charging current of 4 mA under a temperature environment of 23 ° C., and then continuously charged to a constant voltage of 4.2 V until full charge. The constant current constant voltage charging was performed and the initial charge capacity was measured. Then, the final voltage was set to 3 V and discharged, and the initial discharge capacity was measured.

Next, in an environment exceeding room temperature, specifically, 6
The constant current constant voltage charging and discharging were performed in a 0 ° C. temperature environment, and the initial discharge capacity in a 60 ° C. environment was measured. Next, this constant current constant voltage charging / discharging was made into 1 cycle, charging / discharging was repeated 100 cycles, and discharge capacity after 100 cycles was measured. Then, the ratio of the discharge capacity after 100 cycles in the 60 ° C. environment to the initial discharge capacity in the 60 ° C. environment was obtained, and this ratio was taken as the capacity retention rate in the 60 ° C. environment. And 60
From the results of the capacity retention rate under the environment of ° C, the battery characteristics under the environment exceeding room temperature were evaluated.

The above measurement results are shown in Table 1 together with the content of the positive electrode active material and the addition amount of rubidium oxide. A characteristic diagram of the above measurement results is shown in FIG. Note that FIG.
In, the vertical axis is "capacity retention rate under 60 ° C environment"
And the horizontal axis indicates the “addition amount of rubidium oxide”.

[0042]

[Table 1]

From Table 1 and FIG. 2, it can be seen that the capacity retention of Sample 1 provided with the positive electrode to which rubidium oxide was not added did not exceed 0.8. On the other hand, the capacity retention of the other samples including the positive electrode to which rubidium oxide is added is 0.8 or more, which is improved as compared with Sample 1.

The amount of rubidium oxide added is 2% by weight.
Sample 3 as described above has a capacity retention rate exceeding 0.80 in an environment exceeding room temperature, and can be used as a practical battery. From this, the amount of rubidium oxide added is 2
It can be seen that it is appropriate to set the content to the weight% or more.

Further, it is understood that the sample 7 in which the added amount of rubidium oxide is 10% by weight or less has the same capacity retention as the sample 8 in which the added amount of rubidium oxide exceeds 10% by weight. From this, it can be seen that even if the addition amount of rubidium oxide is increased from 10% by weight, the effect of improving cycle characteristics cannot be obtained any more.

Therefore, it is understood that the non-aqueous electrolyte secondary battery has improved cycle characteristics in an environment exceeding room temperature because the positive electrode contains the rubidium compound (rubidium oxide). Further, in the non-aqueous electrolyte secondary battery, the addition amount of rubidium oxide in the positive electrode is in the range of 2% by weight or more and 10% by weight or less,
It can be seen that the battery has a required battery capacity as a practical battery and has improved cycle characteristics in an environment exceeding room temperature.

Samples 9 to 15 The same as sample 1 except that rubidium fluoride was added to the positive electrode and the content of the positive electrode active material and the amount of rubidium fluoride added were changed as shown in Table 2 below. Thus, a non-aqueous electrolyte secondary battery was produced.

With respect to Samples 9 to 15 produced as described above, the first charge / discharge capacity measurements for Samples 1 to 8 were performed in the same manner. Next, the ratio of the discharge capacity after 100 cycles under the temperature environment of 60 ° C. was obtained in the same manner, and this ratio was defined as the capacity retention rate under the environment of 60 ° C. Then, from the result of the capacity retention rate under the environment of 60 ° C., the battery characteristics under the environment of room temperature or higher were evaluated.

The above measurement results are shown in Table 2 together with the amounts of the positive electrode active material and rubidium fluoride added. A characteristic diagram of the above measurement results is shown in FIG. In FIG. 3, the vertical axis represents “capacity retention rate under 60 ° C. environment”, and the horizontal axis represents “addition amount of rubidium fluoride”.

[0050]

[Table 2]

From Table 2 and FIG. 3, each sample in which the added amount of rubidium fluoride is 2% by weight or more and 10% by weight or less has a higher capacity retention rate than Sample 1, and is suitable as a practical battery. I understand. Therefore, in the non-aqueous electrolyte secondary battery, the addition amount of rubidium fluoride in the positive electrode is 2
It can be seen that when the content is in the range of not less than 10% by weight and not more than 10% by weight, the battery capacity required for a practical battery is provided and the cycle characteristics in an environment exceeding room temperature are improved.

Samples 16 to 26 Rubidium sulfate was added to the positive electrode, and the content of the positive electrode active material and the amount of rubidium sulfate added were changed as shown in Table 3 below. A non-aqueous electrolyte secondary battery was produced.

Samples 16 produced as described above
For the sample 26, the first charge / discharge capacity measurement for the samples 1 to 8 was performed in the same manner.
Next, the ratio of the discharge capacity after 100 cycles under the temperature environment of 60 ° C. was obtained in the same manner, and this ratio was defined as the capacity retention rate under the environment of 60 ° C. Then, from the result of the capacity retention rate under the environment of 60 ° C., the battery characteristics under the environment of room temperature or higher were evaluated.

The above measurement results are shown in Table 3 together with the amounts of the positive electrode active material and rubidium sulfate added. A characteristic diagram of the above measurement results is shown in FIG. In addition, in FIG.
The vertical axis represents “capacity retention rate under 60 ° C. environment”, and the horizontal axis represents “addition amount of rubidium sulfide”.

[0055]

[Table 3]

From Table 3 and FIG. 4, each sample in which the added amount of rubidium sulfate is 2% by weight or more and 10% by weight or less has a higher capacity retention than Sample 1, and is suitable as a practical battery. I understand. Therefore, in the non-aqueous electrolyte secondary battery, the addition amount of rubidium fluoride in the positive electrode is 2
It can be seen that when the content is in the range of not less than 10% by weight and not more than 10% by weight, the battery capacity required for a practical battery is provided and the cycle characteristics in an environment exceeding room temperature are improved.

[0057]

As apparent from the above description, the non-aqueous electrolyte secondary battery according to the present invention contains the rubidium compound in at least one of the positive electrode and the negative electrode, and therefore, in an environment exceeding room temperature. The generation of cations other than lithium ions, which contribute to the charge / discharge reaction, which may adversely affect the negative electrode, is suppressed in the positive electrode along with the charge / discharge reaction. Therefore, the non-aqueous electrolyte secondary battery according to the present invention has excellent cycle characteristics under temperature conditions exceeding room temperature.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a non-aqueous electrolyte secondary battery.

FIG. 2 is a characteristic diagram showing the relationship between the capacity retention rate and the amount of rubidium oxide added in a 60 ° C. temperature environment.

FIG. 3 is a characteristic diagram showing the relationship between the capacity retention rate and the amount of rubidium fluoride added in a 60 ° C. temperature environment.

FIG. 4 is a characteristic diagram showing the relationship between the capacity retention rate and the amount of rubidium sulfide added in a 60 ° C. temperature environment.

[Explanation of symbols]

1 non-aqueous electrolyte secondary battery, 2 positive electrode, 3 positive electrode can, 4
Negative electrode, 5 negative electrode can, 6 separator, 7 insulating gasket

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yukio Miyaki             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation (72) Inventor Ken Segawa             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F-term (reference) 5H029 AJ05 AK02 AK05 AK16 AL06                       AL12 AL16 AM03 AM04 AM05                       AM07 BJ03 BJ12 DJ06 EJ01                       EJ04 EJ05 EJ12                 5H050 AA07 BA15 CA02 CA11 CA20                       CB07 CB11 DA01 EA08 EA12                       EA21 EA24 HA01

Claims (5)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material capable of inserting and extracting lithium, and a non-aqueous electrolyte, wherein the rubidium compound is the above-mentioned positive electrode, A non-aqueous electrolyte secondary battery characterized by being contained in at least one of the negative electrodes. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein at least one of rubidium oxide, rubidium fluoride and rubidium sulfate is used as the rubidium compound. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the rubidium compound is contained in the positive electrode. 4. The non-aqueous electrolyte secondary battery according to claim 3, wherein the amount of the rubidium compound added to the positive electrode is in the range of 2% by weight or more and 10% by weight or less. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein carbon capable of inserting and extracting lithium is used as the negative electrode active material.